I can't get Bayes running with postfix!

After following instructions like those at http://advosys.ca/papers/postfix-filtering.html on installing SpamAssassin with postfix, you may find that Bayesian filtering does not function as expected even after installing DB_File and rebuilding the database with sa-learn --rebuild. spamassassin -D --lint indicates no problems.

In those instructions, SpamAssassin is run via a script triggered by a "filter" line in master.cf. The filter is run by a new user, postfilter, rather than as your own user. Changes made to your Bayesian databases are not seen by this user.